The present invention relates to an organic micro-electro mechanical system that can be fabricated within or on the surface of an organic Printed Wiring Board (PWB) utilizing high density interconnect (HDI) substrate technology.
Smaller and more complex electronic devices require smaller switches. Current solid-state switches are not ideal, because they exhibit a finite leakage that precludes a complete xe2x80x9coffxe2x80x9d state. On the other hand, current mechanical and electro-mechanical switches are bulky and consume a large amount of power. Micro electro-mechanical systems (MEMS) have been reported to address the drawbacks of the prior art. See U.S. Pat. No. 5,051,643 to Dworsky and Chason, 1991; and U.S. Pat. No. 5,578,976 to Yao, 1996. However, the above-referenced MEMS are fabricated from crystalline silicon or ceramic silicon dioxide that require fabrication methods (e.g., reactive ion etching, vapor deposition, etc.) that are not compatible with printed wiring board (PWB) fabrication. Therefore, MEMS made by this technology must be made separately, then incorporated into printed wiring boards.
Moreover, crystalline silicon or silicon dioxide ceramic tends to be stiff. Accordingly, these materials are only useful for making switches that have relatively small gaps (e.g., xe2x89xa61 micron), not switches having relatively large gaps (e.g.,  greater than 1 micron), and these switches require a higher activation voltage than switches having a lower elastic modulus. It would be desirable to form MEMS switches that are not based on crystalline silicon or ceramic silicon dioxide.
The organic MEMS according to the present invention can be fabricated during fabrication of the printed wiring board (PWB), and are useful for switches having a wide range of gaps (about 1-25 microns). The organic MEMS comprises a polymeric substrate comprising a substrate surface including a first region and a second region. A polymer coating is applied to the first region to provide a coating surface that is spaced apart from the substrate surface. A terminal is disposed on the second region. A metallic trace is affixed to the coating such that the metallic trace forms a flexible extension over the second region. The extension has a rest position where the extension is spaced apart from the terminal, and a flexed position where the extension is disposed towards the terminal. An actuator is used to provide an electric field to deflect the extension from the rest position to the flexed position. By changing the spacing between the extension and the terminal, it is possible to change the electrical condition provided by the organic MEMS. Because, the extension is not supported by a material such as crystalline silicon or silicon dioxide ceramic, the organic MEMS is compatible with PWB fabrication, and provides a wider range of deflection gaps at a lower activation voltage.
The extension and the terminal need not contact each other to change the electrical condition provided by the organic MEMS. By changing the distance between the extension and the terminal, a variable capacitor is formed, wherein in the rest position, the MEMS has one capacitance, while in the flexed position, the MEMS has another capacitance. The organic MEMS and the method of fabrication are compatible with PWB fabrication and are used to make PWB embedded switches and capacitors.
The present invention is also directed to a method of forming the organic MEMS comprising depositing an electrode at the second region of a polymeric substrate comprising a substrate surface including a first region and a second region, then applying a photopolymer coating over both regions and the electrode. The photopolymer is selectively irradiated in the first region to form an insoluble coating in the first region, while a soluble coating remains in the second region. A metal trace is fixed to the coating such that a flexible extension overlaps the electrode. The soluble coating is removed to expose the electrode such that the electrode is spaced apart from the extension.